Process for the manufacture of armored electric heating elements



y 7, 1940. A. DEROCHE 2.199.879 PROCESS FOR THE MANUFACTURE OF ARMORED ELECTRIC HEATING ELEMENTS Fil'ed June 8, 19:57

INVENTOR A NDRE .UERO CHE ATTY-S.

Patented May 7, 1940 UNITED STATES PROCESS FOR THE MANUFACTURE OF ARMORED ELECTRIC HEATING ELE- BIENTS Andr Deroche, Fontgombaut, France Application June 8, 1937, Serial No. 147,151 In Belgium June 12, 1936 4 Claims.

The present invention relates to a process for the manufacture of armored electric heating elements comprising at least one helically wound conductor separated from an outside armoring by a layer of insulating material.

It is known to compress the above mentioned insulating material by reducing the cross section of the element. This compression is done in order to increase the dielectric and insulating qualities of the material.

In order to prevent deformations of the helically wound conductor during this compression,

, it has been proposed to introduce inside this conductor a metal core made of an alloy of aluminium and magnesium and melting at a relatively low temperature.

After the cross section of the element has been reduced the core is melted out. This melti'ng may give rise to a series of disadvantages and even to accidents if the element is not heated in a perfectly uniform manner over its entire length.

The subject of the present invention is a process obviating these drawbacks.

In the process according to the invention, a metal core hardened by cold working is used, said metal having a low modulus of elasticity when annealed, so that it may be then considerably elongated by a rather small tension without breaking. The said core is annealed after the compression of the insulating material and then elongated.

The appended drawing contains views illustrating the various stages of the process.

Figure 1 is a side view partly in section of an armored heating element with a core inserted therein;

2 is asimilar view of the core; and

Fig. 3 is a similar view after elongation of the' core.

In order to carry out this process, a hard coldworked brass wire 2 is preferably used. It is introduced into the inside of a helically wound conductor wire I insulated from an outside armoring I by a layer of insulating material I. This layer of material is for example a layer of mineral material such as alumina or magnesia.

This brass wire has an outside diameter equal to the inside diameter of the helix formed by the wound conductor wire. 1

Due to the inherent nature of the brass which contains, for example. of copper and 30% of zinc and due to the cold working of this brass the wire employed is very hard and can serve eflectlvcly for preventing any deformation of the Just prior to elongationhelically wound wire during the compression of the insulating material.

The reduction in cross section of the element which causes the compression of the insulating material is carried out for example, by ham- 5 mering.

The hardened cold-worked brass wire which serves as a core for the element during the compression of the insulating material has a length slightly greater than that of the element.

After compression, the element is raised to 'a temperature at least equal to the annealing temperature of'the brass employed. The annealing temperature can be exceeded Without disadvantage. After annealing, the brass has a. low modulus ofelasticity and it is sufficient to pull on the two ends of the brass wire which project from the ends of the heating element, by means of pliers 5 for instance, in order to obtain a considerable elongation of the annealed brass wire. This 20 elongation is accompanied by a uniform reduction ofdiameter. over'the whole length of the brass wire. As a result of this the brass wire 2 may then readily be removed from the heating element which it has served to manufacture.

After the removal of the brass core, the space which it occupied may be filled with insulating material, forv example, by means of powdered alumina or magnesia. The presence of this powder in the space occu- 30 pied by the core may have the effect of facilitating the bending of the heating element.

In view of the advantage of employing a very hard core, it is preferable to use a core which is already very hard before cold working but it is obvious that lack of hardness of the core before cold working may be remedied to. a certain. extent. by more pronounced cold working.

The process applies equally well to all the methods or manufacture of armored resistances, 4 for example those obtained by the conversion in situ of magnesium to its oxide, those where insulating material is introduced into the tube in the form of compressed pastilles (in this case the pastilles are reduced to powder by the reduction 45 in section), or those formed by a paste introduced into the tube.

What I claim is: J l. A method for manufacturing an electric heating element comprising at least one helically wound conductor arranged inside a mass of insulating material enclosed in an outside armoring, said method consisting in introducing inside the helically 'wound conductor embedded in the insulating material a hard metal anvil-forming core 55 tively small tension without breaking after annealing at high temperature, transversally compressing the insulating material against the anvili'orming core, annealing the core, elongating the core alone, removing said core, and tilling the space occupied by it with insulating material.

2. A method ior manuiacturing an electric heating element comprising at least one helically wound conductor arranged inside a mass of insulating material enclosed in an outside armoring. said method consisting in introducing inside the helically wound conductor embedded in the insulating material a hard metal anvil-forming core capable of being considerably elongated by a relatively small tension without breaking after annealing at high temperature. hammering the insulating material against the anvil-forming core, annealing the core. elongating the core alone. removing said core, and iilling the space occupied by it with insulating material.

3. A method for manuiacturing an electric heating element comprising at least onahelieally capable oi being considerably elongated by a relawound conductor arranged inside a mass 0! insulating material enclosed in an outside armoring. said method consisting in introducing inside the heiically wound conductor embedded in the insulating material a brass anvil-forming core hardened by cold working, transversally compressing the insulating material against the anyiliorming core, annealing the core. elongating the core alone, removing said core. and filling the space occupied by it with insulating material.

4. A method for manufacturing an electric heating element comprising at least one helically wound conductor arranged inside a mass of insulating material enclosed in an outside armoring. said method consisting in introducing inside the helically wound conductor embedded in the insulating material. an anvil-forming core of a metal 01' high melting point. transversely compressing the insulating material against the anviliorming core. elongating the core alone. removing saidcore, andiillingthespaceoccupiedbyitwith insulating material.

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